Not sure if you thought of this, but Icelandair do a 1 stop connection from GLA to MSP. And its only £1077 in business class on www.airnet.co.uk! Compared with £700 on BA and similar I think on KL at this short notice. If you want comfort, relatively short flight time, and don't care about the miles, this is worth considering.

If you want the cheapest flight, www.icelandair.co.uk has a farefinder option and incredibly offers GLA-MSP for £210 + £141 tax on certain dates. Similarly business class can be found for £925 plus £161 tax on most dates.